Comparison of disilane and hydrogen adsorption on Si(111)-7×7

Abstract

Multiple internal reflection (MIR) infrared spectroscopy has been used to study the adsorption of H and Si2H6 on the Si(111)-7×7 surface at 200 and 400 K. Both adsorbates react with the Si(111)-7×7 surface to yield a variety of silicon hydrides with similar temperature dependence. Adsorption of atomic hydrogen at 400 K produces three different monohydrides with characteristic vibrational frequencies of 2076, 2086, and 2095 cm−1. At 200 K hydrogen adsorption produces a surface dihydride with a stretching frequency of 2119 cm−1 and a trihydride with a stretch frequency of 2143 cm−1 in addition to the three surface monohydrides. Adsorption of Si2H6 on Si(111)-7×7 at 400 K yields a single absorption feature centered at 2096 cm−1 attributed to surface SiH species. The broad featureless spectrum is indicative of surface disorder due to the deposition of additional surface silicon atoms from the adsorbed disilane. At 200 K the adsorption of Si2H6 yields a sharp vibrational feature at 2154 cm−1 over a broad background centered at 2126 cm−1 characteristic of a surface trihydride species (SiH3). The temperature dependence of the formation of surface hydrides is similar for both adsorbates. Lower adsorption temperatures favor the formation of higher hydrides. Differences are observed in the sequential appearance of absorption bands for adsorption of atomic hydrogen as opposed to the coverage-independent vibrational spectra observed for the adsorption of Si2H6.